In the field of molecular electronics, methods are known such as the nanogap method (C. Li, I-I. He, N. J. Tao, Applied Physics Letters 77, 3995 (2000)) and the break junction method (M. A. Reed, C. Zhou, C. J. Muller, T. P. Burgin, and J. M. Tour, Science 278, 252 (1997), for example, by means of which individual molecules may be contacted. Other methods consist in contacting molecules as a monomolecular layer. One method for the application of molecules as a monomolecular layer involves immersing the substrate (desired carrier for the molecular layer) in a bath composed of molecules and solvent. The Langmuir-Blodgett method (H. Wang, A. Reichert, J. O. Nagy, Langmuir 13, 6524 (1997)) may also be used for producing monomolecular layers.
In the use of monomolecular layers it is disadvantageous that only complete layers or layer systems can be formed and contacted. This makes it impossible to address individual molecules. Production of a molecular memory matrix by using this method is possible only with great difficulty, since significant effort is required to structure the applied molecular layer. The structural size always depends on the particular structuring method that is the best at the given time. Currently this method is electron beam lithography, by means of which structuring down to 2 nm may be achieved. However, this is a time-consuming sequential method that cannot be used to advance into the region of individual molecules.
Structuring of monomolecular layers entails the risk that the molecules provided as memory elements may be impaired. It is also disadvantageous that molecules applied using the Langmuir-Blodgett method do not form chemical bonds with the electrons. This results in a high molecule-electrode contact resistance and low stability of the molecular layer. It is likewise not possible, using the nanogap method or the break junction method, to form a switching matrix composed of a large number of molecular memory elements.
In principle, it is not possible to use of the above-mentioned methods to integrate multiple molecular contact sites into an nm-dimensional memory matrix. Furthermore, some matrix systems always require two electrode pairs: one pair for “addressing” and one pair for “reading” the information within the molecule. Thus, at present there are only various methods for individual molecules in a targeted manner, but only as individual molecular contact, not as an array.
According to the prior art, thin gold films on mica or gold monocrystals have been used heretofore as bottom electrodes for the contacting of molecules. This is based on the fact that these bottom electrodes provide a low, well reproducible surface roughness, with the gold-sulfur contact being preferred. However, this has the disadvantage that the prevailing CMOS process, in which silicon is used as substrate, cannot be employed.